The extent of roads and other forms of linear infrastructure is burgeoning worldwide, however there has been little quantification of how linear infrastructure affects the movement of water across landscapes. In our paper published in the Journal of Environmental Management, we present the first (to our knowledge) study to characterise and quantify the broad-scale impacts of linear infrastructure networks on surface and near-surface hydrology of a semi-arid region, Western Australia’s Great Western Woodlands.

With linear infrastructure named ‘one of the most pressing rangeland management concerns in arid and semi-arid lands globally’ (Duniway and Herrick 2013, in Rangeland Ecology and Management), we found that hydrological impacts of linear infrastructure are pervasive, but that there is considerable scope for addressing impacts. Hydrological impacts included erosion and pooling, as well as flow impedance, concentration and channelling, diversion, and new channel initiation at drainage crossings. Strategies for managing and mitigating these impacts include: hydrologically considerate infrastructure design; improving consideration of hydrological impacts in environmental impact evaluations, land-use or conservation plans, and mitigation strategies; developing risk maps to inform landscape-scale planning of linear infrastructure in relatively undisturbed landscapes; and further research to better understand the ecological ramifications of the impacts we report, and identify cost-effective solutions.

Our approach and methodology provide information and insights that are useful for cumulative and strategic impact assessment and decision-making as well as landscape planning and conservation policy, and can be applied to a range of other landscapes worldwide.

Examples of linear infrastructure impacts on surface water hydrology. a) Gully erosion along a track caused by large amounts of fast-moving water produced on-road during rainfall events and/or intercepted from upslope overland or subsurface flows. b) A track that is lower than the surrounding ground level has become a drainage channel. c) Three locations 400 m apart along a track where sheetflow from upslope (right of image) appears to have been intercepted by the track, and concentrated into the three drainage outfalls indicated by the arrows. The arrows also show the direction of flow. Vegetation on the downslope (left) side of the track in the lower part of the image appears sparse and may be suffering from water starvation. d) A small eroded channel initiated by a track along which water movement is evident. There is no channel upslope of the track. e) Pooling along a track has created an unnatural water source which has attracted emus (Dromaius novaehollandiae). Wildlife attracted to water along infrastructure are at greater risk of road mortality, and increasing the temporal availability of water for fauna may cause other ecological changes. f) A windrow on the upslope side of a track which intercepted sheetflow and caused upslope pooling, until the windrow was breached and the water flowed onto the track – now in a concentrated fashion. g) Large area of pooling along a track. Such pools can stay wet for many days after the surrounding landscape has dried. Such obstructions to traffic often cause drivers to create alternative vehicle tracks to drive around, causing further disturbance and increasing the total road footprint. In this case the detour track is also flooded and additional detour tracks may result. Images: A, B, D, E, F: Keren Raiter. C: Google Earth. G: Carl Gosper.